The proposed research addresses the problem of renewal of photosensitive membrane in visual cells of the retina. The research is significant because it may contribute to a better understanding of the cellular-molecular mechanisms involved in outer segment turnover. Such knowledge in turn may contribute to understanding pathological processes which result in photoreceptor degeneration. The rationale is that further insights into the mechanisms involved in renewal will require the use of in vitro preparations that can be used in a parametric experimental approach. To this end it is proposed to take advantage of recently developed culture procedures from the Principal Investigator's laboratory which support the light- and dark-dependent processes that result in disc shedding as well as the light-evoked acceleration of disc assembly. Using this system it is proposed to study disc shedding and disc assembly in relationship to culture conditions which permit shedding, to cytoskeletal elements as structures involved in the cellular-mechanical events, to protein and glycoprotein synthesis in photoreceptors, and to a potential role for indoleamine metabolism in the control of disc turnover. In addition, it is proposed that we evaluate the relationship of disc assembly to disc shedding as well as the possibility that the endogenous rhythm which influences shedding is an intrinsic feature of the eye. The approach is experimental and cell biological in nature and involves the coordinated use of a wide range of morphological and biochemical techniques.